1. Field of the Invention
The invention relates to a direct current brushless motor for a fan, especially to a motor in which the position of a sensor is altered a certain distance to obtain a better activation effect.
2. Description of Related Art
With reference to FIG. 5, a conventional direct current brushless motor for a fan has a housing (31), a stator assembly (30) and a rotor assembly. The stator assembly (30) is contained in and fixed with respect to the housing (31). The rotor assembly is contained in and able to rotate with respect to the housing (31). The rotor assembly includes a metal cover (312) under the housing (31), four magnetic sectors evenly arranged under and along the metal cover (312), and a shaft (311). Each magnetic. sector is made up of a permanent magnet (313). The stator assembly (30) consists of four stator poles (301) evenly arranged on a round seat, a sleeve (33), a circuit board (32), and a sensor (321) electrically connected to the circuit board (32) and fixed between two stators poles (301). The round seat covers the sleeve (33). The sleeve (33) is connected to the shaft (311) by a bearing (34). The sensor (321) is used to sense the magnetic strength of the permanent magnets (313) and send signals to the circuit to activate the motor and keep the motor running. Before the motor is activated, the sensor (321) always stops with a sensing window (322) stopping right above where two neighboring permanent magnets (313) meet.
However, this kind of motor has a drawback. The magnetic strength where two neighboring permanent magnets (313) meet is the weakest. Therefore, it is always difficult, or needs a large activation current, to activate the motor.
The main object of the invention is to provide a direct current brushless motor in which the sensing window of the sensor is altered a certain distance to obtain a better activation effect.